Intrathecal Morphine

analgesia pain management spinal anaesthetic Mar 17, 2025

🩺 The heavy hitter - Intrathecal morphine explained

💊 Morphine is a well-known, powerful opioid analgesic, but there are methods of administering it to take its analgesic effect to a whole other level!

🧠 The intrathecal, or subarachnoid space, sits within the spinal canal and is filled with cerebrospinal fluid. When morphine is injected into the intrathecal space via spinal anaesthesia, magic happens! ✨

💧 Morphine is hydrophilic in nature, which means that its concentration within CSF is maintained for far longer when compared to other agents such as fentanyl, which is lipophilic. With intrathecal morphine, the onset of action is roughly 5-10 minutes, with analgesic effects lasting up to 24 hours post a single dose administration! ⏳

🔬 When administered in this way, morphine is able to bypass first-pass metabolism and the blood-brain barrier, meaning that a far smaller dose can achieve excellent analgesic effect, and yield less systemic side effects than seen with oral or intravenous doses. 💉

🩺 When administering intrathecal morphine (ITM):

🚨 Sterile procedure as with any spinal anaesthetic 🦠
🚫 Preservative free morphine must be used 🚫
⚖️ Careful attention paid to the dosing - much smaller than oral/IV dosing ⚖️
💉 ITM can be administered with local anaesthetic, in combination with fentanyl, or as a standalone medication 💉

📊 The standard dosing for ITM ranges from 50 micrograms to 300 micrograms and beyond, it really depends on the patient, the nature of the surgery, the anaesthetist, and the health care facility. 🏥

🏨 Most hospitals will have a specific policy or guideline pertaining to ITM, with a dose threshold warranting HDU observation for the 24-hour duration period - this is usually somewhere between 200-300 micrograms. ⏲️

👀 Close observation of patients who have received ITM is required as adverse effects like respiratory depression can present quite some time post-administration, up to 6-12 hours later. 😷

😖 Sometimes patients still experience acute pain despite the use of ITM, and additional analgesia is required. 💭 Oral opioids may still be used, but are usually prescribed in smaller doses with longer durations between doses to avoid overdose. 🛑 Opioid-sparing adjuncts should be optimised to help reduce the incidence of opioid-related adverse effects. 🌿

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References:

Cosgrave, D., Shanahan, E., Conlon, N. (2017) Intrathecal opioids. WFSA. https://resources.wfsahq.org/atotw/intrathecal-opioids/

Cummings A, Orgill BD, Fitzgerald BM. Intrathecal Morphine. [Updated 2023 Sep 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499880/

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